DrWho,
We are always looking to improve our interoperability where feasible. The STEP file format is more common amongst the Mechanical design industry, however, I will take this request for compatibility with STEP file format to my product manager. Demand is usually the critical factor for such things to be implemented. If you like you should create a post in the Wish area to gauge the community's desire for such a thing.
Our primary interoperability file format for the BIM industry is .IFC (Industry Foundation Classes). Perhaps you can try utilizing files in this format. Learn more at
http://www.openbim.com We can also import 3D dwg files (
http://archicadwiki.com/DWG/Import/3D ) as well as SketchUp .skp files (
http://www.graphisoft.com/products/archicad/addons/google_earth/index.html) .
As for ease of modelling I believe you will find our next release ArchiCAD 16 may change your mind with the new MORPH tool. See the videos for this new feature here:
http://www.youtube.com/playlist?list=PLDD9A4E2E9842BE0E&feature=plcp and here:
http://www.youtube.com/playlist?list=PL1196509B1C879ACD&feature=plcp
Best regards,